Traditional PTT communication starts at an analog two-way radio. Because of the limits of the corresponding technology, a user can select only one among multiple PTT channels (i.e. “analog frequency”) and use the selected PTT channel. The user can listen to a voice input through the selected PTT channel or transmit a voice through the PTT channel. When the user changes the selected PTT channel, the user cannot receive or transmit a voice through the PTT channel before the change, any more.
However, when an IP technology instead of a technology using the analog frequency is applied to PTT communication, a user can simultaneously select multiple PTT channels supported by a PTT terminal and network. The user can receive or transmit a voice through the multiple PTT channels.
In the case where the user simultaneously selects multiple PTT channels, when voices are simultaneously received through the multiple PTT channels and the received voices are reproduced, it is difficult for the user to distinguish the respective PTT channels through which the reproduced voices are received. Moreover, when a user wants to transmit a voice through one PTT channel among multiple PTT channels, a method for selecting a PTT channel to be subject to transmission is needed.
In one example to solve the above, in preparation for the case where a user simultaneously selects multiple PTT channels, the multiple PTT channels may be previously divided into primary PTT channels (or a PTT channel having a relatively high priority) and non-primary PTT channels (or a PTT channel having a relatively low priority). When a voice received through a primary PTT channel is reproduced, even if a voice is received through a non-primary PTT channel, the voice received through the non-primary PTT channel is not reproduced. A PTT terminal notifies the user only the fact that the voice received through the non-primary PTT channel exists.
However, when a voice is received through the primary PTT channel in the course of reproduction of a voice received through the non-primary PTT channel, the PTT terminal stops reproducing the voice received through the non-primary PTT channel and reproduces the voice received through the primary PTT channel.
In the above example, when a voice is continuously received through the primary PTT channel, even if a voice is received through the non-primary PTT channel, the voice received through the non-primary PTT channel cannot be reproduced. In addition, even when voices are not simultaneously received through the primary PTT channel and the non-primary PTT channel, respectively, it is difficult for the user to distinguish between the two PTT channels without the aid of a display device configured to display the two PTT channels.